Merge pull request #86 from SamLau95/refactoring

Fix broken tests
added test file
changed lesson values
replaced methods
changed all_lessons to lesson_values
removed methods
started quiz models
added more specs
fixed quizzes in factories
fixed factories
changed can add method
changed method
finished model specs
changed views
started quiz creation specs
changed lesson to dropdown menu
changed views
changed views
added more quiz specs
removed method